Cluster structures bare metal anions

The efforts to rationalize the formulas and structures of Zintl ions and related species predated extensive definitive structural information on anionic post-transition metal clusters obtained by Corbett and his group in the 1970s [8, 9]. After enough such structural information on the bare post-transition metal clusters became available, the resemblance of their polyhedra to the known polyhedral boranes became apparent. For this reason, the simple Zintl-Klemm concept has been largely superseded by newer, more advanced descriptions of chemical bonding in such clusters, initially those applied to the polyhedral boranes. 

Modem work on these and related bare post-transition element clusters began in the 1960s after Corbett and coworkers found ways to obtain crystalline derivatives of these post-transition element clusters by the use of suitable counterions. Thus, crystalline derivatives of the cluster anions had cryptate or polyamine complexed alkali metals as countercations [8]. Similarly, crystalline derivatives of the cluster cations had counteractions, such as AlCLj, derived from metal halide strong Lewis acids [9]. With crystalhne derivatives of these clusters available, their structures could be determined definitively using X-ray diffraction methods. 

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